Interstellar Travel
Interstellar travel is required if we want to exit the boundary of Solar System and move to other solar systems. However, this is a very hard to do. This article is about current technology. Most of sure future technology will change everything. Technology Current technology offers us a few alternatives. Since they are well detailed on other sites, I will only show some links here. # Orion Project proposed the use of small atomic bombs, to pull a spacecraft. This way, we can achieve up to 10% of the speed of light. # Fission Engine can produce the same thrust as Orion, but in a continuous jet and not in multiple blasts. # Plasma Engines can produce enough thrust, but they need a source to produce electricity, to power-up the plasma. # Solar Sails might be able to gain enough speed if they are turned very close to the Sun, but never enough speed to reach a nearby star within a human lifetime. # Antimatter Engines might reach enough speed, more then 10% the speed of light, but storing antimatter is extremely dangerous. Also, producing it on a spacecraft, is not feasible. # Chemical Engines are too slow to push a spacecraft to a significant fraction of the speed of light. # Ion Engines have low thrust, not enough for interstellar travel. # Gravity Assists can increase speed, but only up to a limit. Even a system of multiple Jupiter and Saturn gravity assists, culminating with a close Sun flyby, will not be enough to send a spacecraft to reach a nearby star within a human lifetime. There are many other ways of interstellar travel, many of them just under theory of in science fiction. The voyage Once the spacecraft has departed Solar System, it will be completely on its own. It will face the extremely cold of space and will have to shield itself from the interstellar environment and radiations. Also, there is a risk of impact. At such a speed, any collision can be deadly. The probe must generate its own energy for the entire voyage. If a probe reaches 7% of the speed of light and is heading towards Barnard's Star (6 light years), it will travel 86 years. A classic RTG (radioactive thermal generator) will not survive that long. Many devices will cease working. In case of a manned ship, it must also carry the environment needed to sustain life. At the destination (unmanned probe) Let's take a look at the following scenario. We made a space probe. It traveled 86 years and reached Barnard's Star. Now, it is sending us the first ever close images of the system. Signal needs 6 years to reach Earth. The probe will need 12 years to get an answer from us. So, it will be impossible from us to adjust anything. The probe will be completely on its own. Fast flyby When the probe will be twice the orbit of Pluto (10 light hours) from the star, it will be able to scan the sky, searching for planets. Just as the Voyagers made the Solar family Portrait, the probe will make the Barnard Family Portrait and actually see what planets are there. At such a distance, the probe will have 6 days (143 hours) to fly until they reach Barnard's Star. It will be a very fast flyby. The probe will conduct some very fast trajectory correction maneuvers (TCM), so that it will come close enough to the most promising of all planets. All the other planets will be viewed from distance. A habitable planet around Barnard's Star should be around 7 million km from the star, so very close. The probe will be set, like New Horizons, to conduct a very fast flyby. Only that this time it will be even faster. New Horizons could take a low-resolution image of the far side of Pluto, from two million km away. Our probe will not have this chance. Flying with 7% of the speed of light (21 000 km/s), the probe will have only a few seconds to get the closest images from the target planet, to get spectral data, to analyze its magnetosphere and see if it is habitable or not. Onboard cameras will have problems getting high resolution images at such a speed. For comparison, it is like flying from Earth to Moon in 18 seconds or like flying from Earth to the Sun in 114 minutes. For the other planets, the probe will only gather limited information. Most probably the spacecraft will not see other planets as disks, but just as stars, because of their distance. Only limited spectral data can be achieved. Then, the probe will fly away from Barnard's Star and will start to send data back to Earth. When visiting Jupiter, New Horizons needed less then an year to download all data. On Pluto, it needs more then an year, even if the amount of data is far less then on Jupiter. Then, on its final target, MU69, even if it is only an asteroid, New Horizons will need 20 months to download all data. All this, because the signal dissipates through space. Because of distance, only a weak signal reaches back to us. So, the probe will spend decades sending back its findings. A fast flyby mission will resume with: a few close, unclear images and spectral data of a planet, distant spectral analysis of other planets (with no surface details) and science data about the solar wind. Orbiter If we want to get enough data, we need to slow down the ship. Also, if we send a manned ship to colonize a new stellar system, we have to slow down the ship. Let's return to our unmanned probe sent to Barnard's Star. As the probe gets closer, it uses the same engine to slow down. This means that the ship will have to carry all fuel needed with it. So, the mass will increase many times. As the probe reaches twice the distance of Pluto (10 light hours), it slows down and starts to scan the sky for possible planets. It detects them and starts to fly towards them. Since the signal needs 6 years to reach Earth, the probe will decide itself what planet to be visited first. To accelerate to interplanetary movement, the spaceship will use less then 0.1% of the fuel needed for interstellar travel. So, if it still has 1% of its fuel, the ship will be able to visit all planets. So, the probe starts exploring. It visits the first planet, it maps its surface, its chemical composition, its moons, gets information about its atmosphere and magnetosphere, then it goes to the next target. As it moves, the probe keeps scanning for other objects: unseen planets, comets and asteroids. The entire survey of Barnard's Star and its planets might take up to 100 years. Of course, of great interest will be inner planets that can be terraformed. However, there is one important problem. Sending the data back to Earth will be very difficult. As the probe goes further away, radio signal diminishes by the square of distance. So, suppose our probe will send a signal with the same strength as New Horizons, from Barnard's Star, it will be 70 billion times weaker. Sending data at a lower bit rate is a solution, still. It might prove that even after 300 years the probe still will have data to send back from the encounter with the first planet. Sample return A sample return probe will have to detach from Earth, reach 7% of the speed of light, then slow down to interplanetary cruise, visit Barnard's Star, then accelerate back to 7% of the speed of light, return to Solar System and slow down again. If we don't consider fuel mass, the probe will need four times more fuel then for a flyby and twice the fuel needed for an orbiter. However, since it will have to carry all its fuel, the probe will weight probably 20 times more. We might wish to take a small probe from another solar system at least a tiny rock from an asteroid. However, this is not the kind of sample we are talking about. The probe will bring its discoveries home. It could prove more efficient to fly back home then to wait for centuries to send all data back via radio link. While returning, the spacecraft will detach all scientific payload. It will only carry its engine (and fuel), its navigation computer, a navcam (orientation camera) and a CPU with all data stored on. Traveling with 7% of the speed of light, the probe will spend 172 years in interstellar environment and other years inside Barnard solar system. This is why, with current technology, interstellar travel is not feasible. Future technology When spaceships will reach 50% of the speed of light, a one-way trip to Barnard's Star will take 12 years and a sample return mission, spending 10 years there, will need 35 years. At that moment, exploring the nearby stellar systems will become feasible, just like is now exploring of other planets within Solar System. Sending a manned ship towards Barnard System is even more complicated. By using 7% of the speed of light, the trip will take a lifetime. If we get onboard, our grandchildren will reach it. Or, we could travel frozen. If the spaceship moves faster, there is another problem. Ship acceleration is sensed by human body like gravity. Nobody wants to experience an acceleration of over 1G for many days. At an acceleration of 1G (9.8 meters every second), a spaceship reaches 35.28 km/s in an hour and 846 km/s in a day (that is, 2.8% of the speed of light). So, it will take 17 days to reach 50% of the speed of light. A far more advanced technology will not need to worry about acceleration, since they will counter its effects with artificial gravity. Also, it will travel faster then light, with technologies that today we might don't know. Passenger & Cargo After we know what is orbiting the nearby stars, we can think about sending settlers, colonizing and terraforming their planets. Sending people and the needed cargo will require far larger ships then what we need for research. As science and technology makes new discoveries, there will be different types of ships. Zero generation ships A zero-generation ship travels to a nearby star slow, reaching its target in more then a human lifetime. At 18 000 km/s, we need 100 years to reach to Barnard's Star. At 1 800 km/s, we need 1 000 years to reach Barnard's Star. At 180 km/s, we need 10 000 years to reach Barnard's Star. A Soviet sci-fi writer has proposed the use of a comet. On the comet, travelers will use a deuterium fusion reactor for energy, to keep the colony alive. However, 90% of the energy produced will be used for propulsion. The generator will create electricity, used to separate hydrogen and oxygen from water found on the comet. Then, these gasses will be burned to power-up a chemical rocket engine, continuously increasing the speed. Then, after almost 1000 years, when the comet nucleus is exhausted, all what is left is the heart of the colony, that becomes a ship. The ship performs a very close flyby to a gas giant and then to the star. These flybys decrease speed by gravity assist, as well as by aerobreaking. Finally, the ship enters orbit and lands on the target, terraformable planet. Pioneers on a zero-generation ship will be surprised to find other settlers that arrived before them. In 1000 years, space science might evolve to a level that now we are unable to imagine. First generation ships This kind of ships travel with 5% to 10% of the speed of light (just like our hypothetical probe to Barnard's Star). At that speed, settlers can reach their destination within their lifetime. If people are to be kept alive, then the ship must offer all conditions needed for life. If people can be frozen in liquid helium, then the ship can be far smaller. first generation ships will carry people and the basic things needed to start a colony or to begin terraforming. Second generation ships These ships accelerate to 50% or 80% of the speed of light. This way, transport becomes possible much faster between Solar System and the star systems within 10 light years. Traveling close to the speed of light, time passes much slower onboard. At 50% the speed of light, time flows 50% slower. At 80% the speed of light, time flows 80% slower. This means that, at an expected lifetime of 80 years, with 50% the speed of light, someone will actually live 160 years. In this time, it can travel 80 light years. Again, with 80% the speed of light, a person will spend its 80 years in 400 years. In this time, the ship will fly 320 light years. This opens a completely new view on interstellar colonization. Third generation ships The third generation ships will be able to fly above the speed of light. According to Einstein's theory, this is not possible. And even if it would, time on the ship will start flowing backwards. However, 500 years ago nobody thought it is possible to leave the Earth and fly towards the planets. 500 years from now, we might see spaceships traveling faster then the speed of light. Maybe they will alter the fabric of space. Once traveling faster then light becomes possible, colonies can be made anywhere throughout the galaxy. Fourth generation ships These ships will allow us to travel even faster. They will be able to travel away from the galaxy and throughout the entire known Universe. The technology behind them is unknown for us. What we can speculate is that, at such speeds, they will affect the fabric of space. Fifth generation ships NOTE: The following section might require non-linear thinking and knowledge of superior mathematics. Is it possible to go even faster? Let's analyze all the speeds. (<0): Speed below zero - time traveling, back in past (0): Speed zero - static object, fixed to the center of the Universe (0...1): Speed between zero and infinite - any moving object we know (1): Speed equals to infinite - instantly moving (teleporting) (>1): Speed beyond infinite Backwards Time Traveling means that you have to travel slower then zero. Traveling with an average speed means that, suppose you go from point A to point B, you will reach point B in T amount of time. Traveling with a speed slower then zero means that you will reach point B not after T time, but before you start from point A. With other words, traveling with a speed below zero, means that you are traveling backwards in time. Zero Speed Traveling describes the movement of a fixed object. Earth moves, the Solar System moves and the entire galaxy moves. The relative speed of any object is linked to the speed of light. A fixed object in space will face photons moving in all directions with the same speed. Classic Speed of an object, as we know it, is defined as the amount of distance the object passes in a specified amount of time. Everything we know, moves slower or faster. As we well know, speed can be absolute (related to the fabric of space and to the speed of light) or relative (compared to another object, considered to be fixed). Infinite Speed is teleporting. Teleporting means traveling from point A to point B instantly. The amount of time required, T, is zero. So, the speed becomes infinite. By teleporting, we can travel towards any place in the Universe in no time. Faster then infinite is something mind-blocking and not plausible for our brains, even if, in some superior mathematics, sometimes there is something beyond infinite. Two parallel lines are not supposed to meet even at a distance equals to infinite, but beyond that, they can meet. What would mean traveling faster then infinite? Nobody knows. Probably, this will allow us to reach other universes, if they exist. Minus infinite is even harder to accept. This means traveling backwards through time, faster then anything. This will lead a traveler before the moment of creation, into the undefined, a hypothetical environment with no time, no space and no matter. Basically, you will be lost into a nothing, with no way out. You will cease to exist, without time, without space and without matter. I know this sounds like impossible to our day science, just like 1000 years ago people saying the Earth is round, were burned alive. If we think about the world that will be thousands of years from now and mind-blowing scientific discoveries that will arise at that time, theories similar to faster then infinite will be well known, like is today accepted that the Earth is round. Note This article is not well-themed for Terraforming Wiki. I wrote it for two reasons. First of all, before sending people to nearby stars, we must know what is there and to do so, we need to send an unmanned ship first. And second, just accelerating a probe to interstellar speed will not result in much science. Sending a research unmanned probe is the first step. Then, if conditions allow and our grandchildren wish to, terraforming can occur. Category:Technology